(a) "Advertising sign" means a sign which directs attention to a business, commodity or service or entertainment conducted, sold or offered elsewhere than on the premises and only incidentally on the premises, if at all.
(b) "Billboard" means any sign situated on private premises with an area greater than 100 square feet on which the written or pictorial information is not directly related to the principal use of the land on which such sign is located.
(c) "Business sign" means a sign which directs attention to a business or profession conducted on the premises. A "for sale" sign or "for rent" sign relating to the property on which it is displayed shall be deemed a "business sign".